hdftopal: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/hdftopal - from package: hdf

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/hdftopal - from package: hdf4-tools

You may install the required package with command apt-get install {package}

Error in other languages:
hdftopal: bevel nie gevind nie
hdftopal: comandă negăsită
hdftopal: comando não encontrado
hdftopal: commande introuvable
hdftopal: command not found
hdftopal: käsku ei ole
hdftopal: không tìm thấy lệnh
hdftopal: komanda nerasta
hdftopal: Kommando nicht gefunden.
hdftopal: kommandot finns inte
hdftopal: komut yok
hdftopal: nie znaleziono polecenia
hdftopal: níor aimsíodh an t-ordú
hdftopal: no se encontró la orden
hdftopal: no s'ha trobat l'ordre
hdftopal: opdracht niet gevonden
hdftopal: parancs nem található
hdftopal: perintah tidak ditemukan
hdftopal: príkaz nenájdený
hdftopal: příkaz nenalezen
hdftopal: команда не найдена
hdftopal: командата не е открита
hdftopal: 命令找不到
hdftopal: コマンドが見つかりません